“Pages” is indeed a presentation concern, but state isn’t. Often in SSR, user state is stored server side and identified by a cookie. You only need this cookie on the presentation side and not have to store a copy of the whole state like you usually do in a SPA.

In most SPA, state is distributed with two copies floating around. Even if you do restrict the update flow, it’s still a lot of works to keep it consistent. That’s good enough when it’s partitioned and each side take care of its own state, but in most cases, the intersection is very large.

With SSR, the “page” is a dead copy. The only source of truth is the backend.